This grant will define some of the taste qualities of the 5' ribonucleotide monophosphates, inosine monophosphate (IMP) and guanosine monophosphate (GMP) that are important substances used to study "umami" taste. The sense of taste is important for locating food sources, maintaining nutritional equilibrium and avoiding harmful substances. Monosodium glutamate (MSG) is a naturally occurring amino acid present in many protein-rich foods such as meats, cheese, and some vegetables. The ability of an organism to detect glutamate is important because its taste signals the presence of dietary protein, and it can increase the palatability of food and, thus, food intake. Glutamate and several other L-amino acids possess two defining taste qualities. One quality is its unique taste called "umami" that is thought to be distinct from sweet, sour, salty, and bitter. A second defining quality of umami substances is their ability to interact synergistically with IMP and GMP. Surprisingly, even though this synergistic interaction has been and will continue to be key to the study of umami taste, our understanding of the perceptual characteristics of IMP and GMP is limited and almost always intertwined with the study of MSG or other amino acids. These limitations raise two fundamental questions that are the specific aims of this grant: (1) behaviorally how sensitive are rats to IMP and GMP, and (2) do these substances have the same taste qualities as the amino acids that activate umami taste receptors? It is generally assumed that IMP and GMP have an umami taste identical to MSG but there are data suggesting IMP and GMP may possess different taste qualities compared to other umami substances. Behavioral experiments are proposed that address the grant's specific aims. First, experiments will be conducted to determine the detection thresholds for IMP and GMP in rats using standard psychophysical methods. Second, taste discrimination experiments in which rats are forced to detect perceptual differences between two taste substances will be conducted to characterize the taste qualities of IMP and GMP, and to determine if these qualities are distinguishable from MSG and other amino acids. Specifically discrimination experiments will determine whether rats can discriminate between the tastes of IMP, GMP, MSG, and other amino acids with an umami taste. If IMP and GMP have identical taste qualities, and these qualities are the same as MSG and the other "umami" substance. [unreadable] [unreadable]